Assumption Parish Sheriff Mike Waguespack told the Associated Press that Guist was pronounced dead at a hospital on Monday morning; the cause of death is still unclear. He was traveling on the Belle River when he suddenly fell down around 9 a.m. The boat returned to a landing in St. Martin, La., where attempts at resuscitating the History Channel star were unsuccessful.

The History Channel told the AP that Guist would have turned 49 on Friday.

In a statement, the network said:

“We are extremely saddened to report that our friend and beloved member of the Swamp People family, Mitchell Guist, has passed away … Mitchell passed on the swamp, doing what he loved. We appreciate your respect for the Guist family’s privacy and hope you join us in sending our thoughts and prayers to his brother, Glenn, and the rest of the Guist family.”

The hit show follows a group of alligator hunters who live in the Atchafalaya River Basin swamp in Louisiana. Guist was featured on the show alongside his brother Glenn.